A power storage device is configured by accommodating an electrode assembly in which a positive electrode and a negative electrode are stacked via a separator and an electrolyte in a case. In FIG. 3, an example (planar cross-sectional view) of such a power storage device 100 in which an electrode assembly 100b is accommodated in contact with a rectangular case 100a and the case 100a is filled with an electrolyte 100c is illustrated. The power storage module is bonded between end plates in a state in which a plurality of power storage devices configured as described above are arrayed in a predetermined array direction. For example, in Patent Literature 1, a battery assembly in which a plurality of unit batteries between which heat transfer plates are interposed are arrayed in a row and holding plates arranged at both sides of the plurality of unit batteries are fastened by bolts across straightedge rods is disclosed.